The present invention relates to a method and a device for controlling the injection of fuel into an internal combustion engine.
Such a method and such a device for controlling the injection of fuel into an internal combustion engine are known from German Published Patent Application No. 197 12 143, for example. In the procedure described there, fuel injection is divided into a pilot injection and a main injection. Noise emissions can be greatly reduced by a pilot injection.
Pilot injection frequently does not occur in all operating states. This means that in a first operating state there is a pilot injection and in a second operating state there is no pilot injection. In an abrupt switch from one state having pilot injection to an operating state without pilot injection, there is a sudden increase in combustion noise. This increase in combustion noise is perceived by the driver as very irritating.
The procedure according to the present invention makes it possible to greatly reduce the sudden increase in combustion noises in switching from an operating state having a first partial injection and a second partial injection to an operating state without a first partial injection. The first partial injection is preferably a pilot injection which occurs immediately before the second partial injection, also referred to as a main injection.
This is achieved according to the present invention by the fact that before a switch from a first state to a second state without having pilot injection, the noise produced is altered so that the noise emission levels before the switch and after the switch are approximately the same. This is achieved by the fact that the injection data is altered so that even before the switch to the second state, the noise emissions are adapted to the noise emission in the second state. In particular, the duration and/or frequency of the pilot injections is altered.
The pilot injection data is usually selected so that a minimum of noise emission occurs. It has been found according to the present invention that it is possible to adjust the noise by increasing or decreasing the pilot injection quantity. Lengthening the pilot injection duration is particularly advantageous.
In another embodiment, it is possible to provide for the pilot injections to be suppressed continuously more and more frequently in the transition to a state without pilot injection. This means that immediately before the transition every n-th pilot injection is omitted. The number n is decreased slowly to a value of 1 according to a certain scheme starting from a large value. This means, for example, that at the beginning, one in ten injections is suppressed, and at the conclusion of the transition all injections are suppressed.